Potentiodynamic methods of following up intercrystalline corrosion

This paper is concerned with a potentiodynamic polarization method based on reactivation from passive state. The suggested test method was verified on austenitic chrome-nickel and chrome-nickel-molybdenum steels with a stepped-up carbon content. For the purpose of adjusting the sensitivity of the new method, intercrystalline corrosion tests were simultaneously carried out using a standard solution in the presence of copper filings. The tendency of the individual steels to intercrystalline corrosion was assessed on the basis of determined intercrystalline corrosion regions in terms of temperature and the sensitization period, the so called Rollason curves.The ratio of charge during reactivation to that in the active region of the polarization curve (at increasing potential) expressed in percent appears the optimum quantitative criterion of the tendency of steels to intercrystalline corrosion. The sensitivity of the method can be adjusted for the individual types of steel by changing the experimental conditions, in particular temperature and potentiochange rate, as well as by the type or specific chemical composition of the electrolyte.     

Nanoscale structure intercrystalline interactions in fat crystal networks

The functional attributes of fat-structured food products such as butter, margarine, chocolate, and ice cream are strongly influenced by the structure and physical properties of an underlying fat crystal network present in the material. Fat crystal networks are arranged in a hierarchical manner with characteristic and quantifiable nano and mesoscale structures. Recent studies carried out by our group have demonstrated that the formation of such a fat crystal network starts with the association of nanoplatelets at the lowest constitutional level. These nanoplatelets interact and aggregate via van der Waals's forces into larger fractal structures, which eventually form a 3-dimensional network responsible for the solid-like characteristics of the material. The purpose of this review is to summarize recent efforts in the characterization and quantification of these recently discovered crystalline nanoplatelets and to discuss the role of van der Waals interactions between them. In addition a brief discussion of previous fractal model will be presented. The new experimental findings on the nanostructural level will then be used to validate our fractal structural–mechanical model of fats (Marangoni, 2000). These new insights will contribute to our knowledge of the nature of fat crystal network in plastic fats at different length scales and the relationship of these structural characteristics to the function and properties of fats.     

Benzenoid links

In this paper, we study new configurations of benzenoid hydrocarbons, called benzenoid links. Roughly speaking, a primitive corofusene is a closed narrow hexagonal ribbon with out-of-plane curvature 0. A primitive corofusene or the union of disjoint primitive corofusenes in mathbbR³{mathbb{R}^{3}} is called a benzenoid link. In this paper, we determine the minimum number of hexagons needed for a nontrivial benzenoid link in different senses. We also determine the structures of the smallest and the second smallest nontrivial benzenoid links of different types and their numbers of Kekule structures. We list all the benzenoid Hopf links of type III with 22–25 hexagons by their canonical codes in the appendix.     

On Borromean links

n-Borromean links are nontrivial links in whichn rings,n 3, are combined in such a way that any two component rings form a trivial link. The symmetry of links withn = 3 is discussed, and it is shown that such links form a variety of series whose members are different isotopy types. Examples are adduced of 3-Borromean links that are topologically chiral: Novel constructions are described ofn-Borromean links with and without at least one nontrivial sublink.     

Dynamic nanoscale Borromean links

Employing halogen atom labels on one of the ligand precursors, the lability of at least some of the 30 dative and 12 imine bonds stabilizing and constituting the three rings of a metallo-Borromean linked compound are scrambled in acidic methanolic solution.     

Enumerating DNA polyhedral links

With the fast-growing of DNA self-assembly techniques, a large number of DNA catenanes or more specifically, DNA polyhedral links were synthesized in the past decade. As a sequel of a recent paper (J. Math. Chem. 50, p. 1693, 2012) by the present authors on the enumeration problem of polyhedral links, this paper considers the enumeration problem of DNA polyhedral links. In contrast to a general molecular link, a DNA polyhedral link has four notable features: 1. the memory of DNA chain direction; 2. the accurate DNA complementary base pairing; 3. the twist patterns of the double-helical strands; 4. the migration in branched junction. These features put forward particular requests for treating the enumeration problem of DNA polyhedral links. In addition to using the standard Pólya’s counting theory, we here introduce the generating function and edge direction retentivity analysis to the enumeration problem, by which we establish explicit expressions of the numbers of DNA polyhedral links for three typical models. These models have been used as strategies or are potential strategies in the synthesis of DNA polyhedral links.     

Visual observation of contact-induced intercrystalline migration of aromatic species adsorbed in zeolites by fluorescence microscopy.

Intercrystalline migration and a migration-assisted chemical reaction of adsorbed aromatic species between zeolite particles in physical contact were visualized by fluorescence microscopy coupled with a particle manipulation technique. The luminescence color characteristics of particular zeolite particles originating from the specific photochemistry of adsorbed species was exploited to follow the migration of the molecules. Two examples are shown that are relevant to the visualization of the time-dependent migration process: A one guest-two sets of zeolite crystals system: chrysene (Chry)-loaded zeolite Na+ -X (the sodium form of zeolite X) crystals were placed in contact with unloaded Tl+ -X (thallium-exchanged X) crystals and allowed to stand at room temperature. Initially, the blue fluorescence of Chry was detected only from the Na+ -X particles, but later, the development of green phosphorescence emission was discernible from the Tl+ -X which suggests that Chry migrated from the Na+ -X to the Tl+ -X crystals. A two guest-species systems: Electron-donating Chry-loaded Na+ -X crystals were placed in contact with electron-accepting 1,2,4,5-tetracyanobenzene (TCNB)-loaded Na+ -X or Na+ -Y crystals. With time, the former system (Chry/Na+ -X and TCNB/Na+ -X) gave rise to the emission of Chry-TCNB charge-transfer complexes resulting mainly from the migration of Chry while the latter system (Chry/Na+ -X and TCNB/Na+ -Y) afforded the same emission resulting largely from the migration of TCNB. The present investigation reveals that there is a certain direction for guest migration depending on the zeolite host and the nature of host-guest or guest-guest interaction.     

Fabrication of a nano-sized ZSM-5 zeolite with intercrystalline mesopores for conversion of methanol to gasoline

Carbon deposition during methanol to hydrocarbons leads to the quick deactivation of ZSM-5 catalyst and it is one of the major problems for this technology. Decreasing the crystal size or introducing mesopores into ZSM-5 zeolites can improve its diffusion property and decrease the coke formation. In this paper, nano-sized ZSM-5 zeolite with intercrystalline mesopores combining the mesoporous and nanosized structure was fabricated. For comparison, the mesoporous ZSM-5 and nano-sized ZSM-5 were also prepared. These catalyst samples were characterized by XRD, BET, NH3-TPD, TEM, Py-IR and TG techniques and used on the conversion of methanol to gasoline in a fixed-bed reactor at T = 405 °C, WHSV = 4.74 h-1and P = 1.0 MPa. It was found that the external surface area of the nano-sized ZSM-5 zeolite with intercrystalline mesopores reached 104 m2/g, larger than that of mesoporous ZSM-5(66 m2/g) and nanosized ZSM-5(76 m2/g). Catalytic lifetime of the nano-sized ZSM-5 zeolite with intercrystalline mesopores was 93 h, which was only longer than that of mesoporous ZSM-5(86 h), but shorter than that of nanosized ZSM-5(104 h). Strong acidity promoted the coke formation and thus decreased the catalytic lifetime of the nano-sized ZSM-5 zeolite with intercrystalline mesopores though it presented large external surface that could improve the diffusion property. The special zeolite catalyst was further dealuminated to decrease the strong acidity. After this, its coke formation rate was slowed and catalytic lifetime was prolonged to 106 h because of the large external surface area and decreased weak acidity. This special structural zeolite is a potential catalyst for methanol to gasoline reaction.     

The braid index of polyhedral links

Polyhedral links have been used to model DNA polyhedra and protein catenanes. Some topological characteristics of a type of polyhedral links fabricated from a polyheron by the method of ‘n-branched curve and X-tangled covering’ have been elucidated. In this paper, we pay close attention to their braid index considered significant in view of DNA nanotechnology, and proved that the MFW inequality is sharp for the polyhedral links. Our results demonstrate that the braid index of the links is directed by their crossing numbers. In addition, the studies of the polyhedral links can facilitate the research of the properties of DNA molecules, and can characterize their structural complexity.     

The architecture of Platonic polyhedral links

A new methodology for understanding the construction of polyhedral links has been developed on the basis of the Platonic solids by using our method of the ‘n-branched curves and m-twisted double-lines covering’. There are five classes of platonic polyhedral links we can construct: the tetrahedral links; the hexahedral links; the octahedral links; the dodecahedral links; the icosahedral links. The tetrahedral links, hexahedral links, and dodecahedral links are, respectively, assembled by using the method of the ‘3-branched curves and m-twisted double-lines covering’, whereas the octahedral links and dodecahedral links are, respectively, made by using the method of the ‘4-branched curves’ and ‘5-branched curves’, as well as ‘m-twisted double-lines covering’. Moreover, the analysis relating topological properties and link invariants is of considerable importance. Link invariants are powerful tools to classify and measure the complexity of polyhedral catenanes. This study provides further insight into the molecular design, as well as theoretical characterization, of the DNA polyhedral catenanes.     

Topological chirality and achirality of links

Empirical and analytical methods employed in the detection of topological chirality and achirality (amphicheirality) in oriented and non-oriented links are critically examined.U-polynomials of non-oriented links are modified for use in the detection of topological chirality. By use of this method, all but eight (listed below) non-oriented links with up to four components and nine crossings are proven to be topologically chiral, including 4 ₁ ² , the abstract model of the only topologically chiral, non-oriented catenane (chemical link) synthesized so far. The topological chirality of certain 3-Borromean links is similarly proven. The amphicheirality of 2 ₁ ² 6 ₂ ² 8 ₈ ² 9 ₆₁ ² 6 ₃ ² 8 ₄ ³ 8 ₆ ³ and 8 ₄ ³ is proven by the demonstration that all eight non-oriented links can attain rigidly achiral presentations. Furthermore, we conjecture that 9 ₆₁ ² and a two-component, oriented link with an 11-crossing diagram are the first members of, respectively, a class of non-oriented and a class of oriented amphicheiral, non-alternating, prime links with odd crossing numbers. Amphicheirality combined with an odd crossing number is unprece dented among knots or links.     

Nanoscale Borromean links for real

Borohydride reduction of a Borromean Ring (BR) complex containing six zinc(II) ions and 12 imine bonds has resulted in its demetallation, producing a neutral BR compound and also its free macrocycle, following cleavage of at least one of the imine bonds in the ethanolic reaction mixture.     

The HOMFLY polynomials of odd polyhedral links

This paper extends the methodology for the construction of odd polyhedral links. Building blocks are odd chain tangles, each of which consists of finitely many $2n+1$ -twist tangles for any nonnegative integer $n$ . For any polyhedral graph $G$ , replacing each edge with an odd chain tangle results in an infinite collection of odd polyhedral links. The relationship between the HOMFLY polynomials of these odd links and the $Q^{d}$ -polynomial of $G$ is established. It leads to the determination of the span of the HOMFLY polynomial, the bound on the braid index and the genus of each odd link. Our results show that these indices depend not only on the building blocks but also on the graph $G.$      

Architecture of Platonic and Archimedean polyhedral links

A new methodology for understanding the construction of polyhedral links has been developed on the basis of the Platonic and Archimedean solids by using our method of the ‘three-cross-curve and dou- ble-twist-line covering’. There are five classes of polyhedral links that can be explored: the tetrahedral and truncated tetrahedral links; the hexahedral and truncated hexahedral links; the dodecahedral and truncated dodecahedral links; the truncated octahedral and icosahedral links. Our results show that the tetrahedral and truncated tetrahedral links have T symmetry; the hexahedral and truncated hexahedral links, as well as the truncated octahedral links, O symmetry; the dodecahedral and truncated dodeca- hedral links, as well as the truncated icosahedral links, I symmetry, respectively. This study provides further insight into the molecular design, as well as theoretical characterization, of the DNA and protein catenanes.     

The Homfly polynomial of double crossover links

Motivated by double crossover DNA polyhedra (He et al. in Nature 452:198, 2008; Lin et al. in Biochemistry 48:1663, 2009; Zhang et al. in J Am Chem Soc 131:1413, 2009; Zhang et al. in Proc Natl Acad Sci USA 105:10665, 2008; He et al. in Angew Chem Int Ed 49:748, )2010, in this paper, we construct a new type of link, called the double crossover link, formed by utilizing the “ $n$ -point star” to cover each vertex of a connected graph $G$ . The double crossover link can be used to characterize the topological properties of double crossover DNA polyhedra. We show that the Homfly polynomial of the double crossover link can be obtained from the chain polynomial of the truncated graph of $G$ with two distinct labels. As an application, by using computer algebra (Maple) techniques, the Homfly polynomial of a double crossover tetrahedral link is obtained. Our result may be used to characterize and analyze the topological structure of DNA polyhedra.     

Hydrocarbon links in an octet truss

We use the octet truss of R. Buckminster Fuller to develop a geometric placement method for synthesizing braid representations of knots and links of oligo (phenylene ethynylene)s using the 60° ortho, 120° meta or 180° para phenyl ring substitution angles and respecting the van der Waals repulsion constraints. We show that any knot or link can be realized by a phenylene ethynylene oligomer modeled on the octet truss. Use of this lattice is motivated by the structural constraints of these phenylene ethynylene units. Where in bio-organic chemistry, questions often involve identifying existing knots, for example in DNA strands, organic synthesis is concerned with assembling molecular structures that can be verified to exist in a desired knot topology. This physical realization of a knot as a construction of common organic molecular subunits then facilitates further study of the properties of knotted molecules in general.     

‘Weak links’ in polystyrene

A first step in the thermal degradation of polystyrene prepared by radical polymerisation has been isolated by heating the polymer in the temperature range 199–280°C. In this step a chain scission process occurs without formation of volatile products, involving, on average, about one bond between structural units in every 10 000. This gives more direct evidence than hitherto of the presence of ‘weak links’ in polystyrene which are shown to be randomly distributed in the polymer chains, their scission resulting in a single break in the molecule of polystyrene to which they belong.The very low energy of activation for chain scission suggests that more than one rate determining step is involved in the process.     

Synthesis and properties of polysulfonamides containing thiophene links

In order to study the synthesis and properties of polysulfonamides containing thiophene links, 2,2-bis(5-chlorosulfonyl-2-thienyl)propane [BCTP], 2,2-bis(5-chlorosulfonyl-2-thienyl)butane [BCTB], 1,1-bis(5-chlorosulfonyl-2-thienyl)cyclohexane [BCTC], and 2,4-dichlorosulfonyl thiophene [DCST] were prepared and interfacial polycondensations with various aliphatic diamines were carried out. The resulting polymers had inherent viscosities in the range of 0.13–0.41 dL/g and showed high extent of moisture absorptions. Most of the polysulfonamides were soluble in electron-donating solvents such as pyridine, DMF, DMSO, NMP, etc. These polysulfonamides exhibited relatively good thermal stabilities. The TGA data revealed 5% weight losses at 275–405°C and residual weights at 500°C were 13–40% under nitrogen. It was also found that dithienyldisulfonyl chlorides produced more thermally stable polymers than DCST, which were comparable to common polysulfonamides from aromatic disulfonyl chlorides.